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Planet MySQL
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Planet MySQL - http://www.planetmysql.org/
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Beware of svctm in Linux’s iostat
I’ve been studying the source of iostat again and trying to understand whether all of its calculations I explained here are valid and correct. Two of the columns did not seem consistent to me. The await and svctm columns are supposed to measure the average time from beginning to end of requests including device queueing, and actual time to service the request on the device, respectively. But there’s really no instrumentation to support that distinction. The device statistics you can get from the kernel do not provide timing information about device queueing, only a) begin-to-end timing of completed requests and b) the time accumulated by requests that haven’t yet completed. I concluded that the await is correct, but the svctm cannot be.
I just looked at the sysstat website, and it has been updated recently to warn about this, too:
svctm
The average service time (in milliseconds) for I/O requests that were issued to the device. Warning! Do not trust this field any more. This field will be removed in a future sysstat version.
Related posts:How Linux iostat computes its resultsHow to find per-process I/O statistics on LinuxSoutheast Linux Fest is around the cornerRecap of Southeast Linux Fest 2009How to auto-mount removable devices in GNU/Linux
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Farewell CHM, hello EPUB!
For a long time, the MySQL Documentation Team has been providing CHM files for most MySQL documentation we publish. Like many other formats, CHM-format docs can be downloaded from http://dev.mysql.com/doc. CHM (Compiled HTML Help) has been the de facto standard help file format on Windows since 1997, but the technology behind it is outdated and has all kinds of quirks. The successor format introduced with Windows Vista is AP Help, but it hasn't taken off in practice so far. So, with CHM being outdated and AP Help spread anything but widely, lots of vendors have started providing documentation on Windows in PDF or HTML format.Building CHM-format documentation is a challenge of its own. I'll not go into details here, so let me just state that it requires a dedicated Windows box (or VM), and while it can be automated using Power Shell commands, there's no way to find out whether or not a CHM file was built correctly, except by manual inspection. This makes it different from all other documentation formats where technical QA is done (successfully) in an automated fashion.With the increasing complexity and size of our documentation (the MySQL 5.1 Manual contains more than 1.6 million words now!), providing CHM has become more and more of a pain, because builds tend to break more often. We've stopped shipping CHM with the MySQL Server on Windows months ago because we simply couldn't guarantee that the help file shipped with the software would work. Also, we're running short on hardware resources, so we'd rather stop wasting the resources we have on building a format that's of limited use, anyway.This is why we'll stop providing CHM for any of the documentation we publish.To alleviate potential pains anyone might have with this decision, let me tell you that we've started providing EPUB-format docs. EPUB (see http://en.wikipedia.org/wiki/EPUB) is an open standard format for screen readers, mobile or not, and is fairly easy (and not resource-intensive!) to compile. Thanks to Lenz for suggesting to build EPUB!Go to http://dev.mysql.com/doc to grab MySQL documentation in EPUB format. To read EPUB on desktop machines, I use a Firefox add-on, unsurprisingly called epubreader, which loads EPUB documents fast and renders them nicely. That said, please be aware that EPUB can't do anything about the fact that the MySQL Reference Manual is huge, so downloading it to a mobile device can take a while. The MySQL 5.1 Manual is currently a whopping 15 MB!
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VLDB 2010
I will be at VLDB 2010 next week. If anyone on this blog is attending and wants to catch up to discuss start ups and innovation in DB, NoSQL, Big Data etc drop me a line and I will try to meet up.
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MySQL Workbench 5.1
MySQL Workbench 5.1 (5.1.19 GA, published on Monday, 06 Sep 2010)
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XS4ALL offer IPv6 connectivity to retail customers
Good news. I was told by a colleague that the Dutch ISP XS4ALL is offering IPv6 connectivity to its retail customers. You can see here although the comments are in Dutch. They also provide a list of ADSL routers which should work for their service. The Cisco name may not be surprising but this is good publicity for Draytek and AVM FRITZ!box for their products. Hopefully it will also stimulate other SOHO router providers into the act to get their names on the list. Let us hope that more ISPs start to offer this sort of service to their customers.
I’m not sure if there’s a list of residential ISPs in each country which provide IPv6 connectivity. If not it might be worth making one and updating it as new providers off this service.
I checked my ISP, Jazztel, and was not really surprised to see that neither technical support or the sales staff really new what I was talking about when I asked if they were planning on offering IPv6 support. That’s unfortunate, but I don’t think any other Spanish ISP is any better. That is any other residential ISP in Spain. I expect some of the larger bigger ISPs are likely to off this to business customers.
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